connected--perhaps through some
action of the plotting rivals.

And then, gently at first, but with increasing intensity, the solid
ground on which they were all standing seemed to rock and sway, to
heave itself up, and then sink down.

"Bless my--" began Mr. Damon, but he got no further, for a mighty gust
of wind swept out of the tunnel, and blew off his hat. That gust was
but a gentle breeze, though, compared to what followed. For there came
such a rush of air that it almost blew over those standing near the
opening of the great shaft driven under the mountain. There was a roar
as of Niagara, a howling as in the Cave of the Winds, and they all bent
to the blast.

Then followed a dull, rumbling roar, not as loud as might have been
expected, but awful in its intensity. Deep down under the very
foundations of the earth it seemed to rumble.

"Run! Run back!" cried Tom Swift. "There's a back-draft and the powder
gas is poisonous. Stoop down and run back!"

They understood what he meant. The vapor from the powder was deadly if
breathed in a confined space. Even in the open it gave one a terrible
headache. And Tom could see floating out of the tunnel the first wisps
of smoke from the fired explosive. It was lighter than air, and would
rise. Hence the necessity, as in a smoke-filled room, of keeping low
down where the air is purer.

They all rushed back, stooping low. Mr. Damon stumbled and fell, but
Koku picked him up and, tucking him under one arm, as he might have
done a child, the giant followed Tom to a place of safety.

"Well, Tom, it went off all right," said Mr. Job Titus, as they stood
among the shacks of the workmen and watched the smoke pouring out of
the tunnel mouth.

"Yes, it went off. But did it do the work? That's what we've got to
find out."

They waited impatiently for the deadly vapor to clear out of the
tunnel. It was more than an hour before they dared venture in, and then
it was with smarting eyes and puckered throats. But the atmosphere was
quickly clearing.

"Switch on the lights," cried Tom to Tim, for the illuminating current
had been cut off when the blast was fired. "Let's see what we've
brought down."

Following the eager young inventor came the contractors, some of the
white workers, Mr. Damon and Professor Bumper. The little scientist
said he would like to see the effect of the big blast.

Along they stumbled over pieces of rock, large and small.

"Some force to it," observed